The objective of this work is to develop radioassays which will measure specific forms of folate. Toward this end we are investigating the binding properties of various macromolecules extracted from tissues as well as attempting to immunize animals with specific folates coupled to macromolecules. With antibodies or natural binders of specific folates, we will develop competitive binding radioassays using isotopically labeled folate analogue. We will then study the concentration of each folate analogue in serum, red cells, and other tissues.